This disclosure relates to wheel speed sensing systems and in particular to a sensing system that can determine the rotational speed of each wheel of an axle. More specifically, the disclosure is directed to an internally housed two-channel wheel speed sensor assembly for smaller sized axle housing that does not rely on speed sensor systems on each wheel axle shaft.
Vehicles typically include an axle assembly having a housing or case and a differential assembly. The housing includes a cavity into which the differential assembly is positioned. The differential assembly is mechanically coupled to the vehicle engine by an input drive shaft and is also coupled to the vehicle drive wheels via a pair of wheel axle shafts. The differential assembly regulates drive torque between the wheel axle shafts, thereby permitting the shafts to rotate at different velocities such as when one of the drive wheels is slipping or when the vehicle is turning.
Speed sensor assemblies for vehicles are used to monitor the rotational speed of the wheels for various purposes such as for implementing antilock or automatic braking system (ABS), traction control systems, and/or as input to an engine or transmission controller. A speed sensor can be employed to sense the rotational speed of a wheel or another component, such as the axle shaft, which has the rotational speed of the wheel.
Wheel speed sensors are often placed near the differential assembly or around the axle shaft and inside the differential housing or case to protect the speed assembly from exposure. Wheel speed sensor systems can be one-channel or two-channel systems depending on the number of speed sensors present. In one-channel systems, the wheel speed is determined by a single speed sensing the speed of the rotating differential ring gear or other rotating component of the differential which provides the an average speed of the two opposing wheels of the axle. Two-channel systems typically utilize two speed sensors, one for each wheel. Wheel speed sensors installed at the axle shaft ends can be positioned nearest to the wheels but this can result in exposing the speed sensor assembly to unfavorable condition which can impede their function and longevity.
One-channel wheel speed sensor systems are typically being used in axle assemblies with smaller sized axle housings since there is limited space to mount speed sensor assemblies on each wheel axle shaft. Typical smaller capacity axle housings are the so-called banjo-type housings which have gained popularity. Banjo-type housings have found use in medium and heavy duty vehicles. However, the average wheel speed outputted by one-channel wheel speed systems are of limited use to anti-lock and traction control systems that require knowing the rotational speed of each wheel or equivalently their respective wheel axle shaft to function properly.